Recreational and commercial water systems, as well as natural bodies of water, e.g., ponds, are subject to contamination from the presence and growth of microbes, e.g., algae, pathogenic bacteria and fungi. The sanitization of standing or recirculating water systems often involves introducing a hypochlorite anion donor material, such as calcium hypochlorite, into the water system so as to establish a desired level, e.g., a sanitizing amount, of free available chlorine (FAC) within the water system. The presence of free available chlorine serves to eradicate or control deleterious amounts of microbial species that are present in the water comprising the water system. Sanitation of water contacted by humans and animals is required because exposure to unsanitized or inadequately sanitized water that contains deleterious amounts of pathogenic bacteria, fungi, viruses, protozoa, etc can lead to the development of infection or disease.
Recreational bodies of water, e.g., swimming pools, hot tubs, spas, etc are generally treated with chlorine-containing sanitizers so as to contain free available chlorine (FAC) in amounts of from 1 to 3 parts FAC per million parts of water [ppm, (sometimes reported as milligrams per Liter, mg/L)]. Water having an FAC content in amounts of greater than 10 ppm (generally in the range of hundreds to thousands of mg/L) can be used to sanitize surfaces or articles to which it is applied, e.g., surfaces of equipment or tables used for the preparation of food. Free available chlorine (FAC) can be established in an aqueous system by adding regularly a source of hypochlorous acid (HOCl) or hypochlorite anion (ClO−), e.g., calcium hypochlorite, to the water comprising the aqueous system.
Hypochlorous acid or hypochlorite anion can be introduced into water to be sanitized by passing the water, or a portion thereof, through a container that contains calcium hypochlorite, e.g., calcium hypochlorite in the form of granules, tablets or other shaped forms. Alternatively, calcium hypochlorite, e.g., granular calcium hypochlorite, can be added directly to water that is to be treated, e.g., sanitized. When water is introduced into the container containing the calcium hypochlorite, it dissolves, thereby forming an aqueous solution comprising hypochlorite anion, which solution is mixed with the water to be treated.
In the case of a standing or recirculating body of water, e.g., a swimming pool, periodic batch additions of higher levels of hypochlorite anion can be made to the body of water in addition to the relatively steady and lower level additions described previously. Such batch additions of higher levels of hypochlorite anion are commonly referred to as a “shock treatment” or as “superchlorination” and are made on a periodic basis, e.g., once a week, once a month, or as required by problems or conditions arising in the pool or spa, such as high bather loads, algae blooms, high rainfall, fecal release accidents, etc. The purpose of a shock treatment is to briefly increase the FAC of the water to, e.g., 5 to 20 mg/L, to consume accumulated organic material, destroy chloramines and/or control algae blooms or pathogen infestations. A shock treatment is administered by, for example, preparing a concentrated aqueous solution of calcium hypochlorite and adding this concentrated solution to the water, or distributing, e.g., broadcasting, an appropriate amount of particulate calcium hypochlorite directly over the surface of the water.
Calcium hypochlorite is an oxidizer that can cause or enhance the combustion of organic materials by providing oxygen for combustion. In accordance with US Department of Transportation (DOT) regulations; namely, Title 49, Code of Federal Regulations (CFR), part 173, section 127, paragraph (a), subparagraph (1), [49 CFR §173.127(a)(1)], calcium hypochlorite is categorized as a Division 5.1 oxidizer. More particularly, it is classified as a Packing Group II oxidizer material [49 CFR §173.127(b)(ii)]. The transport of a material categorized as a Division 5.1 oxidizer requires the use of special precautions, which can include the use of special containers.
Further, the National Fire Protection Association (NFPA) classifies calcium hypochlorite having greater than 50% free available chlorine as a Class 3 oxidizer. NFPA Class 3 oxidizers can require separate free standing storage facilities and/or special sprinkler systems. Depending on the volume of water that is to be sanitized, the amount of calcium hypochlorite that is stored on site can be large. Hence, the requirements for storing and handling large amounts of conventional calcium hypochlorite can involve substantial costs.
It is, therefore, desirable to develop a solid calcium hypochlorite composition that is not classified as a DOT Packing Group II Division 5.1 oxidizer (or a Class 3 NFPA oxidizer), but rather can be classified as a DOT Packing Group III Division 5.1 oxidizer (or a Class 2 NFPA oxidizer), more desirably as a DOT non-Division 5.1 oxidizer (or a Class 1 NFPA oxidizer). It is also desirable that such a solid calcium hypochlorite composition have a FAC content at least sufficient to allow its practical use in the batch and/or continuous sanitization of water systems, e.g., standing or recirculating water systems such as a swimming pool, spa, hot tub, cooling tower water, evaporative condenser, etc.